This invention relates to a catalyst composition useful for converting a C9+ aromatic compound to a C6 to C8 aromatic hydrocarbon and to a process for using the composition in a hydrodealkylation process.
It is well known to those skilled in the art that aromatic hydrocarbons are a class of very important industrial chemicals which find a variety of uses in petrochemical industry. Recent efforts to convert gasoline to more valuable petrochemical products have therefore focused on the aromatization of gasoline to aromatic hydrocarbons by catalytic cracking in the presence of a catalyst. The aromatic hydrocarbons produced by the aromatization process include C6 to C8 hydrocarbons such as benzene, toluene and xylenes (hereinafter collectively referred to as BTX) which can be useful feedstocks for producing various organic compounds and polymers. However, heavier, less useful aromatic compounds are also produced during the aromatization process. It is, therefore, highly desirable to convert these compounds to the more useful BTX.
Furthermore, a catalyst used in the hydrodealkylation of these heavier aromatic compounds is generally deactivated in a rather short period because of depositions of carbonaceous material such as, for example, coke on the surface of the catalyst.
Accordingly, there is an ever-increasing need to develop a catalyst and a process for converting these heavier and less useful aromatic compounds (mainly trimethyl- and tetramethylbenzenes) to the more valuable BTX hydrocarbons (hereinafter referred to as hydrodealkylation process) and, in the meantime, for suppressing the coke formation. Such development would also be a significant contribution to the art and to the economy.
An object of this invention is to provide a catalyst composition which can be used to convert a C9+ aromatic compound to a C6 to C8 aromatic hydrocarbon. Also an object of this invention is to provide a process for producing the catalyst composition. Another object of this invention is to provide a process which can employ the catalyst composition to convert C9+ aromatic compounds to C6 to C8 aromatic compounds. An advantage of the catalyst composition is that it decreases coke deposits thereon and exhibits high hydrodealkylation activity, satisfactory selectivity to xylenes, and good stability. Other objects and advantages will becomes more apparent as this invention is more fully disclosed hereinbelow.
According to a first embodiment of the present invention, a composition which can be used as a catalyst for converting a C9+ aromatic compound to a C6 to C8 aromatic hydrocarbon is provided. The composition is a metal oxide-promoted alumina having incorporated therein a coke suppressor wherein the metal of the metal oxide is selected from the group consisting of cobalt, molybdenum, nickel, rhodium, palladium, platinum, chromium, tungsten, and combinations of any two or more thereof.
According to a second embodiment of the invention, a process for producing a composition which can be used as catalyst in a hydrodealkylation process is provided. The process comprises (1) contacting a metal oxide-promoted alumina with a coke suppressor precursor selected from the group consisting of silicon-containing compounds, phosphorus-containing compound, boron-containing compounds, magnesium-containing compounds, tin-containing compounds, titanium-containing compounds, zirconium-containing compounds, molybdenum-containing compounds, germanium-containing compounds, indium-containing compounds, lanthanum-containing compounds, cesium-containing compounds, and combinations of any two or more thereof under a condition sufficient to incorporate the coke suppressor into the metal oxide-promoted alumina to form a modified metal oxide-promoted alumina; and (2) calcining the modified metal oxide-promoted alumina under a condition sufficient to convert the coke suppressor precursor to its oxide form wherein the amount of coke suppressor precursor is the amount that is sufficient to be converted to a coke-suppressing amount when said composition is used in a hydrodealkylation process.
According to a third embodiment of the present invention, a process which can be used for converting a C9+ aromatic compound to a C6 to C8 aromatics compound is provided which comprises, consists essentially of, or consists of, contacting a fluid which comprises a C9+ aromatic compound, optionally in the presence of an insert fluid such as a hydrogen-containing fluid, with a catalyst composition which is the same as disclosed above in the first embodiment of the invention under a condition effective to convert a C9+ aromatic compound to an aromatic hydrocarbon containing 6 to 8 carbon atoms per molecule.